DENTALIUM. 



and sometimes extending considerably along the superior 

 part of the tube, and from this circumstance Lamarck 

 has named one species 2>. Fissura. Besides this fissure, 

 these species, when perfect, have a small semicircular 

 appendage projecting posteriorly from each side of the 

 aperture : these do not appear to have been observed 

 before ; we have, therefore, given a magnified representa- 

 tion of the posterior extremity of D, Fissura, which shows 

 them more distinctly than any other species we have 

 seen. 



There are many recent species of Dentalium, some 

 of which are much more nearly cylindrical than others ; 

 some are ventricose, others have a slight constriction 

 near, or at the anterior aperture: they are all marine, 

 and several are found on our coasts. Of fossil species 

 there are also many, particularly in the marine beds of 

 the tertiary formations; the London Clay and the Cal- 

 caire grossiere swarm with several sorts not easily distin- 

 guishable from the recent species, among which, we may 

 particularly remark the fossil species from Piacenza, 

 which so nearly resembles D. elephantinum, that Brocchi 

 has not hesitated to refer it to that species, and the Ebur- 

 neum of Lamarck, which he says inhabits India, and is 

 found fossil at Grignon. 



In our plate we have given 



Fig. 1. D. elephantinum, Lam. Recent. 



2. The same fossil, according to Lam. and Brocchi. 



3. D. Fissura, Lam. 



4. A magnified portion of the posterior extremity. 



5. D. circinatum. 



6. D. eburneum. 



7. D. Gadus. 



8. The same magnified. 



9. We do not venture to assert that these also are Dentalia, but we have 

 given a drawing of them in our plate, because of their great similarity in form; 

 they are of a corneous, not a shelly substance, closed at the larger end and 

 attached to each other by a similarly corneous ligament ; what they are we do 

 not even dare to guess; for we are constrained to acknowledge that, in our 

 opinion, scarcely any subject is involved in more impenetrable obscurity than the 

 real nature of the Dentalium, on account of our not being acquainted with ita 

 animal inhabitant. 



